Unless the inconvenient expedient of frequent manual adjustment at the individual heat outlets is resorted to, it is not possible to operate present-day multi-outlet heating systems, in particular central heating systems, in the most efficient and economical manner. For example, in a hotel, present-day systems do not enable a bedroom to be heated only to a low temperature when unoccupied, and heated to a suitable higher temperature when it is about to be occupied.
French Pat. No. 2,264,256 discloses a system for heating hotels in which the heating in any room is turned on when the key for that room is removed from a central bank of hooks in a reception area and is turned off when the key is returned to its hook. Such an arrangement is disadvantageous in that (a) there is no provision for low level heating when the room is unoccupied, whereby rooms can become excessively cold if unoccupied for more than a short period, and (b) it cannot function properly in conjunction with a time switch arrangement often employed in heating systems to control the heat outputs of the heat outlets at different levels during a predetermined period of time, for instance 24 hours.
DE-OS No. 2,530,855 discloses an arrangement in which heat levels in different rooms can be selectively controlled from a central location. However, it does not teach an arrangement in which selective central heat control and overall time switch control are provided in a manner in which such two forms of control are fully compatible and in particular in a manner in which an unoccupied room or group of rooms can be heated at a low level without having to effectively disconnect the time switch control from the heat outlet or outlets heating that room or group of rooms.